Induction of cytochrome P450IA1 in rat colon and liver by indole-3-carbinol and 5,6-benzoflavone.

It is known that consumption of cruciferous vegetables protects against the chemical induction of cancer in many organs. It has been suggested that this protection is mediated through an effect on the cytochrome P450 monooxygenase system. This system is responsible for the activation of a number of chemical carcinogens to their ultimate forms. In the present study, the effect of indole-3-carbinol (I3C) and 5,6-benzoflavone (5,6BF) on the expression of cytochrome P450IA1 in rat colon and liver has been investigated. Cytochrome P450IA1 mRNA was induced in colon following a single oral administration of I3C or 5,6BF. A biphasic induction profile was obtained with maxima at 4 and 16 h post-administration. Both inducers caused an approximately 2-fold increase in P450IA1 mRNA at 4 h and a 10-fold increase at 16 h. In contrast, both cytochrome P450IA1 and IA2 mRNAs was increased over the control between 4 and 24 h. The total amount of P450IA mRNAs in liver at 4 and 16 h was increased about 2- and 4-fold respectively by I3C; 5,6BF induced the P450IA mRNAs 4- and 5-fold respectively. The expression of cytochrome P450IA1 and IA2 is induced by I3C and several flavones present in cruciferous vegetables. This suggests that one of the protective effects of cruciferous vegetables in the reduction of chemically induced cancer may be regulation of cytochrome P450s involved in the metabolism of the chemical carcinogens.